This invention relates to valve seats that are made of a sintered Fe-base alloy that has high wear resistance, that is less hostile to valve and that hence is suitable for use with internal combustion engines such as diesel engines and gasoline engines, particularly those having high power outputs.
Japanese Patent Public Disclosure No. 178073/1983 describes a valve seat made of a copper-impregnated Fe base alloy sinter that has Cu infiltrated in a sintered Fe base alloy substrate having a porosity of 6-14 vol % and structure such that Cr base alloy particles that contain 2-30% C (unless otherwise specified, all percents are by weight), 7-15% Co, 15-25% W and 1-8% Fe, with the balance being Cr and incidental impurities, and 8-12 vol % of Fe-Mo alloy particles are dispersed in an Fe base alloy matrix that contains 0.1-1.9% Mo, 0.5-2.5% Ni, 4.5-7.5% Co, 3-6.5% Cr, 0.5-1.7% C and 1-2.7% W, with the balance being Fe and incidental impurities.
Because of the use of superchargers and multiple valves, as well as the increase in rotational speeds, modern internal combustion engines are designed to produce higher power outputs, causing an ever growing increase in both thermal and mechanical loads. If such modern internal combustion engines are equipped with a valve seat made of the aforementioned conventional copper-impregnated Fe base alloy sinter, the Cr base alloy particles and Fe-Mo alloy particles dispersed in the Fe base alloy matrix, although they are very hard, have only poor adhesion to the Fe base alloy matrix and, during the operation of the engine, those alloy particles will be oxidized and dislodged, causing the valve seat to wear. Further, the dislodged alloy particles will also cause the mating valve to wear.